The present disclosure relates generally to satellite communications, and more specifically to systems and methods for accurate antenna pointing in satellite communications.
An Earth-based antenna terminal for communication with a satellite typically has high antenna gain and a narrow main beam pointed at the satellite, because of the large distance to the satellite and to avoid interference with other satellites. Mobile antenna terminals include a positioner (or other pointing adjustment mechanism) to maintain pointing (or tracking) of the beam of the antenna at the satellite during movement.
Pointing error (or misalignment) between the boresight direction of maximum gain of the beam and the actual direction of the satellite can have a detrimental effect on the quality of the link between the antenna and the satellite. Small misalignment may be compensated for by reducing a modulation and coding rate of signals communicated between the antenna and the satellite. However, to maintain a given data rate (e.g., bits-per-second (bps)), this approach may increase system resource usage and thus result in inefficient use of the resources. Pointing error can also make it more challenging to ensure compliance with interference requirements with other satellites that are imposed by regulatory agencies (e.g., FCC, ITU, etc.) and/or a coordination agreement with operators of the other satellites.
The pointing error may increase with time due to various factors such as drift of a sensor (e.g., an inertial reference unit (IRU)) associated with mobile antenna terminal, structural deflections caused by movement and other disturbances, etc. In order to correct this pointing error, the mobile antenna terminal may occasionally perform a signal-based mispointing correction operation such as steptrack, conical scan and similar methods. The mispointing correction operation can include moving the beam of the antenna in an attempt to determine the direction at which a signal metric (e.g., signal strength) of a signal communicated with satellite is maximized.